About Trees

Excerpted from Scientific American “Earth Talk,” July 20, 2015 (read the full article here):

Trees are known to improve air quality by capturing pollutants and toxic gases. In fact, a single tree can absorb 10 pounds of air pollutants per year. In a study published in 2014, U.S. Forest Service scientists and collaborators calculated that trees are saving more than 850 human lives a year and preventing 670,000 incidents of acute respiratory symptoms. The researchers valued the human health effects of the reduced air pollution at nearly $7 billion every year.

More recently, a 2015 study from the Centre for Research in Environmental Epidemiology (CREAL) in Barcelona, Spain found that children exposed to more greenery—as measured by satellite imagery of their schools and neighborhoods—demonstrated better attention skills and memory development. While the association was partly mediated by reductions in air pollution, Mark Nieuwenhuijsen, one of the study’s authors, noted that he and the study’s other researchers don’t think it’s all air pollution: “I think it’s also some kind of direct effect… you see quite a beneficial effect of green space on mental health.”

A large recent study builds on a body of prior research showing the cognitive and psychological benefits of nature scenery — but also goes farther in actually beginning to quantify just how much the addition of trees to a neighborhood enhances health outcomes. The researchers, led by psychologist Omid Kardan of the University of Chicago, were able to do so because they were working with a vast dataset of public, urban trees kept by the city of Toronto — some 530,000 of them, categorized by species, location, and tree diameter — supplemented by satellite measurements of non-public green space (for instance, trees in a person’s back yard).